In situ δ13C and δ18O microanalysis by SIMS: A method for characterizing the carbonate components of natural and engineered CO2-reservoirs

Abstract

This work addresses the potential utility of in situ carbon and oxygen isotope microanalysis (δ 13 C and δ 18 O) by secondary ion mass spectrometry (SIMS) in carbon sequestration research. A desirable long-term consequence of CO 2-injection into underground rock formations at prospective sequestration sites (such as deep saline sandstone aquifers capped by impermeable strata) is the precipitation of carbonate mineral cements, the isotopic fingerprinting of which is a central theme here. More specifically, we focus on the unique advantage of the SIMS technique, which lies in the capability of analyzing very small sample volumes that are otherwise inaccessible to sampling techniques in conventional isotope ratio mass spectrometry (IRMS). For example, single carbonate crystallites as small as 3-10 µm across can be readily analyzed by SIMS with sub per-mil (‰) accuracy and precision. Importantly, the ability to perform micrometer-scale measurements in situ from either thin sections or 1-inch (25 mm) diameter polished core plugs preserves the petrographic context of measured carbonate δ 18 O and δ 13 C values. We provide a preliminary characterization of the pre-injection mineralogy and isotopic fingerprints of carbonate cements in the Mount Simon Sandstone reservoir and the overlying shaly caprock (the Eau Claire Formation) at the Illinois Basin Decatur Project, a demonstration and research site for exploring the feasibility of long-term CO 2 storage in a deep saline aquifer. By drawing upon published data on ambient reservoir conditions and the isotopic composition of the injected CO 2 , we make simple predictions regarding possible δ 13 C values of calcite, dolomite-ankerite, and siderite cements that may form in response to long-term CO 2 storage.

Determination of carbon isotopes in carbonates (calcite, dolomite, magnesite, and siderite) by femtosecond laser ablation multi-collector ICP-MS

“…In situ C isotopic analyses by secondary ionization mass spectrometry (SIMS), 7–12 NanoSIMS 13 and laser ablation coupled to multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) 14 have received increased interest in Earth science-related studies, which provides valuable isotopic information of geological samples at a high resolution. For example, single carbonate crystallites (dolomite-ankerite) as small as 3–10 μm across can be readily analyzed by SIMS with a sub per-mil (‰) accuracy and precision (2s).…”

“…For example, single carbonate crystallites (dolomite-ankerite) as small as 3–10 μm across can be readily analyzed by SIMS with a sub per-mil (‰) accuracy and precision (2s). 10 The micron-scale C isotope signatures of magmatic calcium carbonate (calcite) have been successfully measured using ns-LA-MC-ICP-MS with a satisfactory precision (within 0.50‰; 2SD). 14 Due to the complex chemical and physical features of natural carbonate, efforts have been made to calibrate a series of dolomite-ankerite solid solution reference materials for C isotope microanalysis using SIMS.…”

Detecting and quantifying palaeoseasonality in stalagmites using geochemical and modelling approaches

“…However, recent improvements in this area, alongside improvements in sample preparation techniques have been substantial enough to enable accurate correction for instrumental drift (Valley and Kita, 2009). The impact of trace element content on carbonate d 18 O and d 13 C analyses also requires careful consideration (Sliwinski et al, 2017), but can be corrected following careful standardisation and is generally not a problem encountered through speleothem analysis where the trace element content is typically less than 1 weight %. An emerging analytical frontier concerns the impact of water and/or organic content on SIMS carbonate d 18 O and d 13 C, requiring careful pre-screening of sample material and simultaneous analysis of OH-and CH-respectively (Orland et al, 2012;Orland et al, 2015;Orland et al, 2019;Wycech et al, 2018).…”

Atomic spectrometry update – a review of advances in environmental analysis

“…The great advantage of SIMS for research into carbon sequestration is its ability to analyse very small sample volumes. For example, in situ δ 13 C and δ 18 O measurements could be made 485 on single carbonate crystallites as small as 3-10 µm in width with sub per-mil (‰) precision and accuracy. The study focused on characterising the mineralogy and isotopic fingerprinting of underground rock formations prior to CO2-injection and made predictions regarding the δ 13 C values of carbonate mineral cements that may form in response to long-term storage of CO2.…”